Expression analysis of genes regulated by RBPJ (Notch) and Axin2 (Wnt) mediated signaling in mouse cardiogenesis at E9.25

Progenitor cells of the first and second heart fields (FHF and SHF) depend on cardiac-specific transcription factors for their differentiation. In mouse mutant embryos, we define the hierarchy of signaling events that controls the expression of cardiac-specific transcription factors during commitment of SHF progenitors at E9.25. Wnt and Bmp act downstream of Notch/RBPJ at this developmental stage. Mutation of Axin2, the negative regulator of canonical Wnt signaling, enhances Wnt and Bmp signals and suffices to rescue the cardiac differentiation arrest caused by loss of RBPJ. By analysis of isolated cardiac progenitors, embryo cultures in the presence of pharmacological inhibitors, and Bmp triple mutants, we could classify the expression of heart-specific transcription factors of SHF progenitors according to their dependence on either Wnt or Bmp signals, Nkx2-5, Isl1, Baf60c and Gata4, SRF, Mef2c, respectively. Total RNA from whole embryonic hearts of control mice was compared to MesP1-cre:RBPJlox/lox (KO), MesP1-cre:RBPJlox/lox//Axin2-/- (DKO), MesP1-cre:RBPJlox/+//Axin2-/- (hetDKO) and MesP1-cre:RBPJlox/lox//Axin2+/- (DKOhet) mutant mouse embryos.